1. Field of the Invention
The present invention relates to a compact zoom lens composed of a plurality of lenses.
2. Description of the Related Art
A high zoom ratio and compactness is consistently required in a zoom lens for a 35 mm lens shutter camera. To satisfy these requirements, Japanese Patent Application Laying Open (KOKAI) No. 64-88512 shows a zoom lens composed of four lens groups respectively having negative, positive, positive and negative focal lengths and having a zoom ratio about three times. In the case of this zoom lens, a ratio of a maximum entire length and a focal length at a telescopic end is equal to about 0.9 so that the zoom lens is compact and an F-number (F/No) on a telescopic side is equal to about 6 showing a bright state.
However, a zooming operation is mainly performed by a fourth lens group in this zoom lens. The fourth lens group has a short focal length and a moving amount of this fourth lens group is large. Therefore, it is necessary to dispose a mechanical mechanism for moving the fourth lens group by a large moving amount, which is disadvantageous to make a lens body tube compact. Further, the fourth lens group is constructed by three lenses to reduce the generation of aberration. The fourth lens group approaches an image face at a wide angle end of the zoom lens so that it is necessary to increase a lens diameter. Accordingly, it is disadvantageous to construct the fourth lens group by three lenses in view of cost, weight and space. It is also very disadvantageous to make the lens body tube compact in consideration of the large moving amount of the fourth lens group. This zoom lens has a diaphragm in a second lens group in which a light beam on an optical axis of the zoom lens is widened. A diameter of the diaphragm is increased so that the lens body tube is large-sized.